Optical viewing and imaging systems require some form of illumination of the object under examination for such purposes as viewing by a human operator, photography of the object, or for machine vision analysis. The ring illumination technique has long been used to provide a good source of even illumination. For example, U.S. Pat. No. 1,444,400 issued in 1923 describes a ringlight using a circular incandescent light bulb.
Fluorescent ring lamps are commonly used today for ringlight systems, as utilized for instance in U.S. Pat. No. 5,247,344. Other techniques for distributing light in a ringlight system have been employed, such as the use of fiber optics, lenses, mirrors, shutters, and prisms, each with their respective benefits and drawbacks. A common feature of these types of ringlight systems is the use of a single, or limited number of light generating sources, which limits the ability to alter the light characteristics under electrical control.
With the advent of inexpensive light emitting diodes (LEDs) has come the use of arrays of LEDs in ringlights. U.S. Pat. Nos. 6,554,452, 6,454,437, 6,141,046, 5,997,164, 5,943,125, 5,926,557, 5,892,539, 5,828,449, 5,820,250, 5,580,163, 4,963,798, and 4,881,802, all include ringlights fashioned from a ring of LEDs. In a refinement of the LED ring concept, multiple concentric rings of LEDs allow selectable angles of inclination of the LED illumination relative to the optical axis by selectively energizing one LED ring or another. Such refinements are described in U.S. Pat. Nos. 6,385,507, 6,238,060, 6,070,986, 5,920,643, 5,576,828, and 5,030,008. In a further refinement, individual LEDs or groups of LEDs within a given single ring allow selectable direction of the LED illumination rotationally around the optical axis by up to 360 degrees. Such ring illumination systems are described in U.S. Pat. Nos. 6,017,133, 5,897,195, 5,690,417, 5,394,246, 5,369,492, and 5,060,065.
The control of these illumination systems varies according to the purpose of the system. For instance, machine vision and process control systems typically use a computer to adjust the lighting as necessary to satisfy a set of recognition criteria. Examples of such systems include U.S. Pat. Nos. 6,774,893, 6,633,338, 6,238,060, 6,017,133, 5,943,125, 5,926,557, 5,828,449, 5,455,870, 5,424,838, 5,420,689, 5,394,246, 5,369,492, 5,030,008, 4,972,093, 4,882,498, 4,706,168, and 4,604,648.
Other illumination systems specify variations on the LED mounting and optical path configuration but do not specify any type of machine or operator control mechanism. Examples of such systems include U.S. Pat. Nos. 6,533,429, 6,385,507, 5,690,417, 5,897,195, 6,273,338, 5,774,212, and 5,060,065.
It is thus apparent that there exists a need for improved control mechanisms that can utilize the various features of the available prior art solutions discussed above.